Abstract:
An extremely halophilic archeon SWO25, affiliated to Haloarcula sp., isolated from sebkha of Ouargla (South Algeria) was screened for secretion of antagonistic substance. To enhance the growth and antagonistic activity, physicochemical conditions were optimized by using a full factorial design. The selected factors were NaCl, MgSO4 and temperature. At first, the antagonistic activity was partially characterized and suitability of Gompertz and Baranyi equations were evaluated for describing archaeal growth curves. The results show that the secreted antagonistic activity has broad spectrum, highest activity was obtained against Halobacterium salinarum and was completely abolished by proteinase K and pronase, suggesting that it is a halocin. The modified Gompertz equation was statistically sufficient to describe the growth data of strain SWO25. Secondary models for Growth rate (μ), lag-time (λ), LnNmax and antagonistic activity (Ac) followed a linear trend with lowest R² greater than 80% and lack of fit not significant (>0.05). A clear interaction effect between NaCl concentration and temperature on growth rate and anti-archaeal activity was shown; this interaction was affected by MgSO4 concentration in the case of antagonistic activity.
Optimal conditions for growth parameters and anti-archaeal activity were different; they were simultaneously optimized at 20% NaCl, 7.5% MgSO4 and a temperature of 45°C. Under these conditions 1.6 and 1.4 fold increase in the specific growth rate and the maximal biomass respectively were reached but there was no further increase on anti-archaeal production. This study contributes to a large-scale biomass and anti-archaeal production for fundamental studies or potential applications.